Studies in the Natural Coating of Apples I. Preparation and Properties of Fractions

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Abstract
The preparation and properties of the major fractions of the natural coating of apples are described. These include the oil, wax, ursolic acid, and"cutin" fractions. Particular attention has been given to the oil fraction, which contains unsaturated esters, and the"cutin" fraction, which gives complex hydroxy acids on saponification. The use of ammonium oxalate for separating apple skin is described. Methods are given for quantitative detn. of the coating fractions. The distr. of these fractions in the cuticle and epidermis is discussed. The oil fraction of the natural coating of Granny Smith apples increased during storage and reached a max. at 3-4 times its original concn. The increase was reduced by"gas" storage (in 5% CO2, 16% O2). Later pickings had a higher oil content. The iodine number of the oil increased with increasing concn. Smaller increases occurred in the wax, ursolic acid, and"cutin" fractions after prolonged storage. The fatty esters of the oil fraction were produced most rapidly at the beginning of storage. Subsequently the production of these non-volatile esters declined, while the rate of volatile ester production increased. There was no definite correlation between the oil content and the resistance of the skin to gaseous diffusion, although both increased during storage.

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